英语听力：自然百科 行星旅行：土星 Saturn—17
时间：2014-08-27 06:23:27
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（单词翻译）
These are just bold first steps on a journey that's just begun.
Even before the mission is over, Cassini has left a thirst for a return trip.
Planetary explorer Jonathan Lunan and
aeronautical1 pioneer Julia Nod think they know the perfect way to do it---a robotic hot air balloon.
So where we are flying over now is very much like the Huygens landing site.
And I love to see those ravines on Titan though steep valleys where the
methane2 is flowing and covering all the hills very much like what we are seeing now.
The dream is to return to Titan and drop a robotic / balloon into the atmosphere.
A radioisotope
generator3 will provide the electrical power and the waste heat to give the balloon lift in the
chilly4 atmosphere.
Titan has a
dense5 atmosphere. It’s cold, the gravity is low, the winds are gentle, so ballooning is very easy.
I think this flight just makes the point so beautifully. Why a balloon is a wonderful way to explore Titan?
If you're over an interesting area, very easy to come down, maybe even land on the surface, lower instruments down.
One could cover with a robotic hot air balloon, the entire
circumference6 of Titan in a space of perhaps six months.
You shouldn't think of Titan as a place just for robots. With a thick protected atmosphere and plenty of frozen water, Titan could be a more user-friendly destination for earthlings than Mars.
When humans do finally move out into the solar system, and I think Titan will be seen as a somewhat distant but very attractive place to go play.
You don't need a pressure suit on Titan, you don't have the feeling as the astronauts described, trying to work with a beachball between your arms
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